Reconfigurable optical add-drop module, system and method

ABSTRACT

An apparatus, system, and method for all-optical wavelength add-drop switching are provided. A number of optical ports, including at least one input port and at least one output port, are each optically coupled to a respective dispersive element. When a multichannel optical signal is input through an input port, an optical beam of each channel emerges from the dispersive element at an angle depending upon its wavelength. The beams emerging from the dispersive element pass through a bulk optical element which redirects each beam toward a respective one of a number of routing or switching elements, each of which has been set to redirect the respective beam through the bulk optical element towards a selected dispersive element coupled to a selected output port.

FIELD OF THE INVENTION

This invention relates to the field of DWDM fibre opticstelecommunications and in particular to the field of all-opticalswitching. The device provides an all-optical wavelength dependenttuneable switching function.

BACKGROUND OF THE INVENTION

The advent of DWDM fibre optics telecommunications systems in the early1990s have enabled a dramatic increase in the transmission capacity overpoint-to-point communication links. This was achieved throughmultiplexing of a large number of individually modulated light beams ofdifferent wavelengths onto the same optical fibre. Typical systemsinstalled today would have 64 or more independent channels preciselyaligned onto an ITU-T standardized grid at 100 GHz, 50 GHz or evennarrower channel spacing. With modulation speeds of routinely 10 Gb/sand attaining 40 Gb/s in laboratory experiments, it is not unusual toobtain aggregated capacities in the order of several terabits per secondof information being transmitted onto a single optical fibre (S. Bigo,Optical Fibre Communication conference, WX 3, Anaheim, 2002). At thesame time, electrical switching capacities have been growing at a muchslower rate, with current largest electrical matrices limited totypically 640 Gb/s in a single stage. Furthermore, in most of theswitching nodes, a large fraction—typically 70%—of the traffic isdistant traffic that just travels through the node. It is thereforeadvantageous to have optical devices with large pass-through capacityand local tuneable drop capability. This device is referred to in theliterature as a Reconfigurable Optical Add-Drop Module or ROADM (J.Lacey, Optical Fiber Communication conference, WT, Anaheim, 2002).

A ROADM usually includes an input port for receiving a DWDM signal, anoutput port for the express traffic and at least one add or drop port(s)for adding or dropping wavelength channels for local processing. This isusually realized through the subsequent steps of demultiplexing theincoming DWDM input, providing an array of switching means to route theindividual channels to either the output express port or the add/dropport, and multiplexing the express channels onto a single output port.Some ROADM have multiplexed add/drop ports, some provide fullydemultiplexed add/drop ports.

It is known to one skilled in the art that multiplexing/demultiplexingtechnologies can be done in many different ways. Serial filterembodiments (Fibre Bragg Grating, Thin Film Filters, fibre Mach Zehndercascade, birefringent filters, etc.) are usually limited in number ofwavelength channels due to insertion loss impairments. Therefore, thetwo solutions of choice currently being developed for ROADM applicationswith a large number of wavelength channels are based on parallelwavelength filtering: either free-space embodiments using bulkdiffraction gratings or waveguide embodiments using AWG (ArrayedWaveguide Gratings).

Free-space optics implementations usually comprise optical fibre ports,lens elements, one bulk diffraction grating and an array of switchingmeans. For example, Corning Inc. from Corning, N.Y., supplies such adevice based on a liquid-crystal switching element. Although showingsuperior optical performances, free-space optics solutions are typicallyexpensive, due to extremely tight alignment tolerances of multiple highprecision optical elements. Furthermore, the relative positioning ofthese elements must be maintained over a wide range of environmentalconditions requiring elaborate opto-mechanical designs.

Paper PD FB 7 presented at OFC'02 in March 2002 in Anaheim, Calif.provides a wavelength selective switch such as shown by way of examplein FIG. 11. The switch includes input coupling optics 1200, switchingelements 1202, a main lens 1204, and a single diffraction grating 1206.Disadvantageously, in this embodiment, only a small part of the serviceof the diffraction grating 1206 lies in the focal plane of the main lens1204. This prevents light beams from all ports to stay in focus.Integrated optics solutions on the other hand have the potential tomaintain the relative positioning of the different elements put onto thesame substrate. There are two main ways of performing parallelwavelength demultiplexing in waveguides: either using AWG or usingEchelle grating, the former being by far the more popular device due tothe difficulty of manufacturing high precision diffraction gratings inwaveguide substrates. Bragg gratings have also been employed for thispurpose.

The AWG was invented by Dragone (C. Dragone, IEEE Photonics TechnologyLetters, Vol. 3, No. 9, pp. 812–815, September 1991) by combining adispersive array of waveguides (M. K. Smit, Electronics Letters, Vol.24, pp. 385–386, 1988) with input and output “star couplers” (C.Dragone, IEEE Photonics Technology Letters, Vol. 1, No. 8, pp. 241–243,August 1989). The AWG can work both as a DWDM demultiplexer and as aDWDM multiplexer, as taught by Dragone in U.S. Pat. No. 5,002,350 (March1991).

An integrated optics ROADM would therefore consist of an input AWG todemultiplex the input DWDM stream, an array of switching means to routethe demultiplexed channels to either an express path or the drop ports,and an output AWG to multiplex the output express DWDM stream. Due tothe cyclic nature of the AWG's filtering function, it is possible to useonly one AWG to perform the ROADM function with some loop back (O.Ishida et al., IEEE Photonics Technology Letters, Vol. 6, No. 10, pp.1219–1221, October 1994). Typically, interconnects in an integratedoptics ROADM are done primarily using guided way optics, for exampleusing waveguides.

The switching elements can either be integrated onto the same substrateas the AWG or can be hybridized. All-integrated embodiments typicallymake use of thermo-optical switches (see for example C. R. Doerr et al.,IEEE Photonics Technology Letters Volume 15, No. 1, January 2003, p 138to 140), taking up a lot of substrate area and requiring careful heatmanagement, eventually limiting its scalability. IntegratedMEMS-waveguide solutions have also been proposed in the past, but theswitching element is usually limited to 1×2 or 2×2, therefore alsolimiting scalability (M. Katayama et al., Optical Fibre Communicationconference, WX4-1, Anaheim, 2001). It is known to a man skilled in theart that hybrid embodiments are possible in which AWG output waveguidesare coupled to MEMS switching elements through a micro-lens array.However, this usually leads to poor spectral performance, i.e. no wideflat channel shape passband (R. Ryf et al., European Conference onOptical Communications, PD B.1.5, Amsterdam, 2001).

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides an apparatuscomprising: a plurality of optical ports including at least one inputoptical port for receiving at least one wavelength channel and at leastone output optical port; for each optical port, a respective dispersiveelement optically connected to the optical port; a bulk optical elementhaving optical power; a plurality of non-transmissive routing elements;wherein for each wavelength channel: the dispersive element of the inputport and the bulk optical element disperses any light of the wavelengthchannel towards a respective one of said plurality of routing elements,and the respective one of said plurality of routing elements directs thelight of the wavelength channel via the bulk optical element to aselected output port of said at least one output port via the respectivedispersive element of the selected output port, the selected output portbeing determined by the respective routing element.

In some embodiments, at least one routing element is also controllableso as to redirect only a portion of a wavelength channel so as torealize an attenuation function.

In some embodiments, at least one routing element is also controllableso as to redirect all of a wavelength channel so as to realize a channelblock function.

In some embodiments, said at least one output port comprises at leasttwo output ports.

In some embodiments, at least one routing element is also controllableso as to redirect only a portion of a wavelength channel so as torealize an attenuation function.

In some embodiments, at least one routing element is also controllableso as to redirect all of a wavelength channel so as to realize a channelblock function.

In some embodiments, the dispersive elements are transmissive and arebetween the optical ports and the bulk optical element having power.

In some embodiments, each routing element is statically configured todirect light to a respective specific output port.

In some embodiments, each routing element is dynamically configurable toswitch light to any output port.

In some embodiments, each dispersive element comprises an array ofwaveguides having a predetermined optical path length difference spreadacross the array.

In some embodiments, the dispersive elements are collectively integratedonto a single waveguide device.

In some embodiments, the dispersive elements are integrated intomultiple waveguide devices.

In some embodiments, the apparatus further comprises micro-opticscoupling elements adapted to couple light from each port to/from therespective dispersive element.

In some embodiments, the apparatus further comprises integrated opticalcoupling elements adapted to couple light from each port to/from therespective dispersive element.

In some embodiments, the integrated optical coupling element comprisestar couplers.

In some embodiments, each dispersive element comprises a transmissivediffraction grating.

In some embodiments, the dispersive elements and the routing elementsare placed substantially at focal planes of the bulk optical elementhaving optical power.

In some embodiments, the bulk optical element having optical power is alens or a curved mirror.

In some embodiments, the dispersive elements are integrated on awaveguide substrate, and the bulk optical element having power comprisesa main cylindrical lens element adapted to focus light in a first planein the plane of the wavelength substrate, the apparatus furthercomprising a transverse cylindrical lens adapted to substantiallycollimate light in a second plane perpendicular to the first plane.

In some embodiments, the main cylindrical lens has a focal length suchthat the dispersive elements are in a focal plane of the lens on a firstside of the lens, and the routing elements are in a focal plane of thelens on a second side of the lens.

In some embodiments, the dispersive elements are selected from a groupcomprising: echelle grating, echellon gratings, prisms, arrayedwaveguides.

In some embodiments, each routing element is a tiltable micro-mirror.

In some embodiments, each routing element is one of a liquid crystalbeam steering element, an acousto-optic beam deflector, part of a solidstate phase array, a controllable hologram, a periodically polledLithium Niobate beam deflector.

In some embodiments, the apparatus further comprises: an athermal mountfor the routing elements adapted to shift the routing elements tocompensate for changes in dispersive characteristics of the dispersiveelements as a function of temperature.

In some embodiments, the apparatus further comprises: an athermal mountfor the dispersive elements adapted to tilt the dispersive elements tocompensate for changes in dispersive characteristics of the dispersiveelements as a function of temperature such that light exiting thedispersive elements is substantially centered on the routing elements.

In some embodiments, the apparatus further comprises: a birefringentcrystal beam displacer between the dispersive elements and the routingelements adapted to compensate for birefringence of the dispersiveelements so as to make TE and TM sub-beams substantially coincide on therouting elements.

In some embodiments, the apparatus further comprises: a quarter waveplate in an optical path of the switch adapted to swap TE and TMsub-beams to cause losses for TE and TM polarization axes to besubstantially averaged out (TE/TM or TM/TE).

In some embodiments, the bulk optical element having power is a lens,each dispersive element is non-transmissive and the optical ports androuting elements are arranged on a first side of the lens and thedispersive elements are on a second side of the cylindrical lens.

In some embodiments, the dispersive elements comprise non-transmissivediffraction gratings.

According to another broad aspect, the invention provides an apparatuscomprising: a plurality of optical ports including an input optical portfor receiving at least one wavelength channel and at least two outputoptical ports; for each optical port, a respective dispersive elementoptically connected to the optical port; a plurality of transmissiverouting elements; a first bulk optical element having optical power; anda second bulk optical element having optical power; wherein for eachwavelength channel: the dispersive element of the input port and thefirst bulk optical element direct any light of the wavelength channeltowards a respective one of said plurality of transmissive routingelements, and an appropriate setting of the respective one of saidplurality of transmissive routing elements directs the light of saidwavelength channel via the second bulk optical element to a respectiveselected port of said at least two output ports via the respectivedispersive element of the selected output port, the selected output portbeing determined by the respective routing element.

In some embodiments, each transmissive routing element is staticallyconfigured to direct light to a respective specific output port.

In some embodiments, each transmissive routing element is dynamicallyconfigurable to switch light to any output port.

In some embodiments, each dispersive element comprises an array ofwaveguides having a predetermined optical path length difference spreadacross the array.

In some embodiments, the dispersive element of the input port isintegrated onto a first waveguide device, and the dispersive elements ofthe output ports are integrated onto a second waveguide device.

In some embodiments, the dispersive element of the input port isintegrated onto a first waveguide device, and the dispersive elements ofthe output ports are integrated onto a stack of waveguide devices.

In some embodiments, the apparatus further comprises micro-opticscoupling elements adapted to couple light from each port to/from therespective dispersive element.

In some embodiments, the apparatus further comprises integrated opticalcoupling elements adapted to couple light from each port to/from therespective dispersive element.

In some embodiments, the integrated optical coupling element comprisestar couplers.

In some embodiments, the dispersive element of the input port is placedsubstantially at a focal plane of the first bulk optical element havingoptical power, and the dispersive elements of the output ports areplaced substantially at a focal plane of the second bulk optical elementhaving optical power, and the routing elements are also at a focaldistance from both the first and second bulk optical elements.

In some embodiments, the first bulk optical element and the second bulkoptical element are each a lens or, a curved mirror.

In some embodiments, the first bulk optical element having powercomprises a first main cylindrical lens adapted to focus light in afirst plane in the plane of first waveguide substrate; the second bulkoptical element having optical power comprises a second main cylindricallens adapted to focus light in a second plane in the plane of secondwaveguide substrate: the apparatus further comprising: a firsttransverse cylindrical lens adapted to substantially collimate light ina third plane perpendicular to the first plane; a second transversecylindrical lens adapted to substantially collimate light in a fourthplane perpendicular to the second plane.

In some embodiments, the first main cylindrical lens has a focal lengthsuch that the dispersive element of the input port is in a first focalplane of the first main cylindrical lens on a first side of the firstmain cylindrical lens, and the transmissive routing elements are in asecond focal plane of the first main cylindrical lens on a second sideof the first main cylindrical lens; wherein the second main cylindricallens has a focal length such that the dispersive elements of the outputport are in a first focal plane of the second main cylindrical lens on afirst side of the second main cylindrical lens, and the transmissiverouting elements are in a second focal plane of the second maincylindrical lens on a second side of the second main cylindrical lens.

In some embodiments, the waveguide dispersive elements are selected froma group comprising: echelle grating, echellon gratings grisms, prisms,arrayed waveguides.

In some embodiments, the apparatus further comprises: an athermal mountfor the routing elements adapted to shift the routing elements tocompensate for changes in dispersive characteristics of the dispersiveelements as a function of temperature.

In some embodiments, the apparatus further comprises: a first athermalmount for the dispersive, element of the input port adapted to tilt thedispersive element of the input port to compensate for changes indispersive characteristics of the dispersive element as a function oftemperature such that light exiting the dispersive elements issubstantially centered on the transmissive routing elements; a secondathermal mount for the dispersive elements of the output ports adaptedto tilt the dispersive elements of the output ports to compensate forchanges in dispersive characteristics of the dispersive elements as afunction of temperature such that light exiting the transmissive routingelements is accurately aligned with the dispersive elements of theoutput ports.

In some embodiments, the apparatus further comprises: a firstbirefringent crystal beam displacer between the dispersive element ofthe input port and the routing elements adapted to compensate forbirefringence of the dispersive element of the input port so as to makeTE and TM sub-beams substantially coincide on the routing elements; anda second birefringent crystal beam displacer between the dispersiveelements of the output port and the routing elements adapted tocompensate for birefringence of the dispersive elements of the outputports so as to make TE and TM sub-beams substantially coincide on therouting elements.

In some embodiments, the apparatus further comprises: a first quarterwave plate in an optical path of the switch on a first side of thetransmissive routing elements adapted to swap TE and TM sub-beams tocause losses for TE and TM polarization axes to be substantiallyaveraged out (TE/TM or TM/TE); a second quarter wave plate in an opticalpath of the switch on a second side of the transmissive routing elementsadapted to swap TE and TM sub-beams to cause losses for TE and TMpolarization axes to be substantially averaged out (TE/TM or TM/TE).

In some embodiments, the dispersive elements are non-transmissive.

According to another broad aspect, the invention provides an apparatuscomprising: a stacked plurality of rows of optical ports, the portscomprising an input optical port for receiving at least one wavelengthchannel and at least two output optical ports; for each optical port, arespective dispersive element optically connected to the optical port; abulk optical element having optical power; a plurality of routingelements; wherein for each wavelength channel: the dispersive element ofthe input port and the bulk optical element disperse any light of thewavelength channel towards a respective one of the plurality of routingelements, and the respective one of the plurality of routing elementsdirects the light of said wavelength channel via the bulk opticalelement to a respective selected output port via the respectivedispersive element of the selected output port, the selected output portbeing determined by the respective routing element.

In some embodiments, each routing element is statically configured toswitch light to a respective specific output port.

In some embodiments, each routing element is dynamically configurable toswitch light to any output port.

In some embodiments, each dispersive element comprises an array ofwaveguides having a predetermined optical path length difference spreadacross the array.

In some embodiments, the dispersive elements of each row arecollectively integrated onto a respective waveguide device.

In some embodiments, the apparatus further comprises micro-opticscoupling elements adapted to couple light from each port to/from therespective dispersive element.

In some embodiments, the apparatus further comprises integrated opticalcoupling elements adapted to couple light from each port to/from therespective dispersive element.

In some embodiments, the integrated optical coupling element comprisestar couplers.

In some embodiments, each dispersive element comprises a diffractiongrating.

In some embodiments, the dispersive elements and the routing elementsare placed substantially at focal planes of the bulk optical elementhaving optical power.

In some embodiments, the bulk optical element having optical power is alens or a curved mirror.

In some embodiments, the bulk optical element having power comprises amain cylindrical lens element adapted to focus light in a first plane inthe plane of the waveguide devices; the apparatus further comprising:for each waveguide device, a respective transverse cylindrical lensadapted to substantially collimate light in a respective second planeperpendicular to the plane of the waveguide device.

In some embodiments, the main cylindrical lens has a focal length suchthat the dispersive elements are in a focal plane of the lens on a firstside of the lens, and the routing elements are in a focal plane of thelens on a second side of the lens.

In some embodiments, the dispersive elements are selected from a groupcomprising: echelle grating, echellon gratings grisms, prisms, arrayedwaveguides.

In some embodiments, each routing element is a micro-mirror tiltable intwo dimensions.

In some embodiments, each routing element is one of a liquid crystalbeam steering element, an acousto-optic beam deflector, part of a solidstate phase array, a controllable hologram, a periodically polledLithium Niobate beam deflector.

In some embodiments, the apparatus further comprises: an athermal mountfor the routing elements adapted to shift the routing elements tocompensate for changes in dispersive characteristics of the dispersiveelements as a function of temperature.

In some embodiments, the apparatus further comprises: an athermal mountfor the dispersive elements adapted to tilt the dispersive elements tocompensate for changes in dispersive characteristics of the dispersiveelements as a function of temperature such that light exiting thedispersive elements is substantially centered on the routing elements.

In some embodiments, the apparatus further comprises: a birefringentcrystal beam displacer between the dispersive elements and the routingelements adapted to compensate for birefringence of the dispersiveelements so as to make TE and TM sub-beams substantially coincide on therouting elements.

In some embodiments, the apparatus further comprises: a quarter waveplate in an optical path of the switch adapted to swap TE and TMsub-beams to cause losses for TE and TM polarization axes to besubstantially averaged out (TE/TM or TM/TE).

According to another broad aspect, the invention provides a wavelengthselective optical switch comprising: a stacked plurality of rows ofoptical ports, the ports comprising an input optical port for receivingat least one wavelength channel and at least two output optical ports;for each row of optical ports, a respective dispersive element opticallyconnected to the row of optical ports; a bulk optical element havingoptical power; a plurality of routing elements; wherein for eachwavelength channel: the dispersive element of the input port and thebulk optical element disperses any light of the wavelength channeltowards a respective one of the plurality of routing elements, and therespective one of the plurality of routing elements directs the light ofsaid wavelength channel via the bulk optical element to a respectiveselected output port via the respective dispersive element of the row ofoptical ports to which the selected output port belongs, the selectedoutput port being determined by the respective routing element.

According to another broad aspect, the invention provides a wavelengthselective optical switch comprising: an input optical port for receivingat least one wavelength channel and a stacked-plurality of rows ofoutput optical ports; for each optical port, a respective dispersiveelement optically connected to the optical port; a plurality oftransmissive routing elements; a first bulk optical element havingoptical power between the dispersive element of the input port and theplurality of transmissive routing elements; and a second bulk opticalelement having optical power between the dispersive elements of theoutput ports and the plurality of routing elements; wherein for eachwavelength channel: the dispersive element of the input port and thefirst bulk optical element direct any light of the wavelength channeltowards a respective one of said plurality of transmissive routingelements, and an appropriate setting of the respective one of saidplurality of transmissive routing elements directs the light of saidwavelength channel through the second bulk optical element to arespective selected output port via the respective dispersive element.

According to another broad aspect, the invention provides an apparatuscomprising: at least two optical ports; a waveguide substrate containingat least two waveguide dispersive elements optically connected to theoptical ports, each waveguide dispersive element comprising a respectivearray of waveguides, the waveguide dispersive elements having a firstlinear phase term for dispersion, and having at least a second parabolicphase term to focus the beam in the plane of the substrate; a free-spacepropagation region; a plurality of switching elements each adapted toestablish a plurality of optical paths through the free-spacepropagation region from any respective first one of the waveguidedispersive elements to any respective second one of the waveguidedispersive elements.

In some embodiments, an apparatus further comprises a transversecylindrical lens which does not affect light propagation in a plane ofthe waveguide dispersive elements, but substantially collimates thelight in a plane perpendicular to the waveguide dispersive elements.

According to another broad aspect, the invention provides an apparatuscomprising: at least three optical ports; for each optical port arespective dispersive element; a bulk optical element having opticalpower optically coupled to all of the ports.

According to another broad aspect, the invention provides a methodcomprising: receiving a light signal through an input port of aplurality of rows of optical ports; for each of a plurality ofwavelength channels: a) dispersing any light of the wavelength channelin the input signal towards a respective one of a plurality of routingelements via a respective dispersive element of the input port and via abulk optical element having optical power; b) the respective routingelement directing the light of said wavelength channel via the bulkoptical element to a respective selected output port of said pluralityof rows of ports via a respective dispersive element of the selectedoutput port, the selected output port being determined by the respectiverouting element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail with reference to theattached drawings in which:

FIG. 1 is a schematic diagram of a known all-integrated waveguide ROADMwith 4 drop ports;

FIG. 2 is a layout view of a known 4 channel all-integrated waveguideROADM with 4 drop ports;

FIG. 3A is a top view of a combined hybrid waveguide and MEMS ROADMembodiment with 4 drop ports and 5 wavelength channels provided by anembodiment of the invention, in which integrated optics provides only anarray of dispersion elements;

FIG. 3B is a side view of the embodiment of FIG. 3A;

FIG. 4A is a top view of a preferred embodiment of a hybrid waveguideand MEMS ROADM with 4 drop ports and 5 wavelength channels as per anembodiment of the invention, in which integrated optics provide an arrayof dispersion elements and an array of coupling optics;

FIG. 4B is a side view of the embodiment of FIG. 4A;

FIG. 5A is a top view of an alternate embodiment of the inventionfeaturing multiple waveguide substrates stacked on top of each other andhaving MEMS elements which are capable of tilting in two dimensions;

FIG. 5B is a side view of the embodiment of FIG. 5A;

FIGS. 6A and 6B is a layout view of an embodiment of the invention wheretwo waveguide devices or waveguide device stacks are used in conjunctionwith transmissive switches capable of steering light beams in twodimensions;

FIG. 7 is a schematic layout view of the waveguide device of the hybridwaveguide and MEMS ROADM of FIG. 4A designed for 40 wavelength channelsat 100 GHz spacing;

FIGS. 8A, 8B and 8C show an example of the modelled far field of thelight exiting the waveguide device of FIG. 7 when a light beam at 192THz, 194 THz and 196 THz is launched through the middle waveguidedispersive element;

FIG. 9A shows an example of a modelling of the near field close to theMEMS array for an input light beam at 194 THz after being focusedthrough a cylindrical lens;

FIG. 9B shows a superposition of near fields close to the MEMS array forlight at 192 THz, 194 THz and 196 THz;

FIG. 10A is a top view of an embodiment of the invention in which themain cylindrical lens is encoded into the phase profile of the waveguidedispersive element with a free-space propagation region between thewaveguide device and the MEMS array;

FIG. 10B is a side view of FIG. 10A.

FIG. 11 is a system diagram of another conventional multi-wavelengthswitch featuring a single diffraction grating;

FIG. 12 is a system diagram of a wavelength selective switch employingfree-space elements and an array of diffraction gratings, provided by anembodiment of the invention;

FIG. 13 is a system diagram of a wavelength selective switch employingfree-space elements, an array of diffraction gratings and a 2Darrangement of optical ports, provided by an embodiment of theinvention;

FIG. 14 is a system block diagram of a wavelength selective switchprovided by an embodiment of the invention featuring temperaturecompensation elements;

FIG. 15 is another embodiment of the invention featuring temperaturecompensation elements;

FIG. 16 is a system diagram of an embodiment of the invention featuringPD lambda compensation; and

FIG. 17 is a system diagram of another embodiment of the inventionfeaturing compensation for PDLoss.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following descriptions like numerals refer to same objects (forFIG. 1 to FIG. 2, and for FIG. 3A to FIG. 10B).

FIG. 1 shows a schematic of a conventional all-waveguide ROADM 100 withone input port 101, one express output 107 e and four tuneable dropports 107 a, 107 b, 107 c, 107 d. A DWDM light beam containing Nwavelength channels λ₁ . . . λ_(N) is input to the input port 101 of thedevice. The different wavelength channels are then demultiplexed by afirst AWG device 102. N outputs from the first AWG device 102 are thencoupled to a switch array 103 of N 1×2 switches 103-1 to 103-N. One ofthe two outputs of each 1×2 switch of the switch array 103 is connecteddirectly to the express output 107 e through an express multiplexer AWG106 e. The other of the two outputs of each 1×2 switch of the switcharray 103 is coupled to a 1×4 switch array containing 1×4 switches 104-1to 104-N. Due to the unavailability of larger switching kernel, each 1×4switch is usually implemented by a 2-stage switching tree made of 3 1×2switches each. In the waveguide shuffle area 105, each of the fouroutputs of the 1×4 switches 104-1 to 104-N is then connected to the dropports 107 a to 107 d through the drop side multiplexers (AWGs 106 a to106 d).

FIG. 2 shows the layout view of a device as in FIG. 1 with fourwavelength channels λ₁ . . . λ₄. The device represents a ROADM 100 withone input, one express output and four drop ports. (see for example C.R. Doerr et al., IEEE Photonics Technology Letters Volume 15, No. 1,January 2003, p 138 to 140) A DWDM multiplexed light beam containingfour wavelength channels λ₁ . . . λ₄ is input to the input port 101 ofthe device. The different wavelength channels are then demultiplexed bya first AWG device 102. The four outputs from the first AWG are thencoupled to an array of four 1×2 switches 103-1 to 103-4. One of the twooutputs of each 1×2 switch of the switch array 103 is connected directlyto the express output 107 e through the express multiplexer AWG 106 e.The other of the two outputs of each 1×2 switch of the switch array 103is coupled to one of the 1×4 switches 104-1 to 104-4. In the waveguideshuffle area 105, each of the four outputs of the 1×4 switches 104-1 to104-4 is then connected to the drop ports 107 a to 107 d through thedrop side multiplexers AWGs 106 a to 106 d. As mentioned earlier, allinterconnects are guided optical paths within waveguides.

It is noted that in the embodiment of FIG. 3A described below, and inall other embodiments, the description deals specifically with droppingwavelength channels. Usually this involves a single input port andmultiple output ports. Alternatively, these same embodiments canfunction to add wavelength channels simply by interchanging the roles ofthe ports. Thus for example, a one input port, four drop (output) portimplementation can equally function as a one output port, four input(add) port implementation.

FIG. 3A shows a top view of a hybrid waveguide and MEMS ROADM 300provided by an embodiment of the invention having one input port 301 c,four drop ports 301 a, 301 b, 301 d, 301 e and five wavelength channelsλ₁, λ₂, λ₃, λ₄, λ₅. The physical ports are any suitable optical portimplementation. For example, each port might be a single mode opticalfibre or a waveguide. An input DWDM light beam containing fivewavelength channels λ₁ . . . λ₅ is input to the device 300 through inputport 301 c. The light beam is coupled to a waveguide device 304 througha micro-optics coupling scheme consisting of cylindrical lens 302 csubstantially collimating the light in the plane of the figure, whileletting the light go through unaffected in the orthogonal plane andcylindrical lens 303 substantially re-focussing the light in the planeperpendicular to that of the figure while letting the light traverseunaffected in the plane of the figure. The cylindrical lens 303 andcylindrical lens 302 a, 302 b, 302 d, 302 e provide coupling optics foroutput ports 301 a, 301 b, 301 d, 301 e respectively. The transformedelliptical light beam (substantially collimated in the plane of thefigure and substantially focussed in the plan perpendicular of thefigure) is coupled to the waveguide region 305 c of a waveguide device304. This waveguide region 305 c consists in an array of waveguidesarranged such that a predetermined path length variation is spreadacross the array. This arrangement is known to a man skilled in the artto provide a waveguide based dispersive element (M. K. Smit, ElectronicsLetters, Vol. 24, pp. 385–386, 1988). Therefore the light exitingwaveguide section 305 c exhibits an angle dependent on the wavelengthaccording to design parameters of the waveguide section 305 c.

Throughout this description, a wavelength channel is an arbitrarycontiguous frequency band. A single wavelength channel might include oneor more ITU wavelengths and intervening wavelengths for example. Eventhough the expression “λ” is referred to herein in respect of awavelength channel, this is not intended to imply a wavelength channelis a single wavelength only.

For ease of description, three out of the five wavelength channels (forexample λ₂, λ₃, λ₄) have been shown in the portion of FIG. 3A to theright of waveguide device 304 although all five would be present at theexit of the waveguide device 305 c. These demultiplexed light beams307-1 to 307-5 first traverse cylindrical lens 306 which does not affectthe light propagation in the plane of the figure, but substantiallycollimate the light in the perpendicular plane. A main cylindrical lenselement 308 is used to focus the light in the plane of the paper, whilenot affecting light propagation in the perpendicular plane, making eachdemultiplexed light beam 307-1 to 307-5 incident upon a switchingelement 309-1 to 309-5. These switching elements in one embodimentconsist of tilting micro-mirrors used to redirect the light at aselectable angle. There can be one tilting micro-mirror per wavelengthchannel.

After reflection from the mirror array 309-1 to 309-5, the light beams307-1 to 307-5 are collimated in a plane perpendicular to the plane ofthe waveguide device 304 by cylindrical lens 306 and are focused in theplane of the waveguide device 304 by cylindrical lens 308. In thepreferred embodiment, the lens 308 is arranged such that the end of thewaveguide device 304 and the switching array 309 are placed at the lensfocal planes, guaranteeing that irrespective of the tilting angle of theMEMS array 309-1 to 309-5, the angle of incidence of the light beams307-1 to 307-5 when they couple back to the waveguide device 304 issubstantially the same as the angle upon exit of the waveguide device304. Therefore when the MEMS tilt angle is controlled in such a way thatthe light beams 307-1 to 307-5 are aligned with any of the waveguidesections 305 a to 305 e, this construction allows for an efficientcoupling and re-multiplexing of the light beams into exiting light beamscoupled to the output ports 301 a, 301 b, 301 d, 301 e through couplingoptics 302 a, 302 b, 302 d, 302 e described earlier.

FIG. 3A shows waveguide dispersive elements in the form of an array ofwaveguides. More generally, an embodiment like that of FIG. 3A canemploy any suitable waveguide dispersive element. For example, one canuse Echelle gratings etched into the waveguide.

FIG. 3A shows micro-optics coupling scheme in the form of cylindricallenses 302 and collimating lens 303. Other micro-optics arrangements canemployed, for example, gradient-index rod lens (Selfoc®, from NSGAmerica) or other types of lens to the same effect.

FIG. 3A shows switching elements in the form of MEMS array 309.Alternatively one can use various other beam steering elements, likeliquid crystal beam steering elements, programmable diffractiongratings, phase arrays, tilting prisms, or moving lens. More generally,routing elements can be employed. Routing elements may perform aswitching function and hence also be switching elements, or may performonly a static routing function.

FIG. 3A shows a cylindrical lens 308 which performs routing between thedispersive elements and the routing elements. More generally, a bulkoptical element having optical power can be employed. For the purpose ofthis description, a bulk optical element having optical power can be acurved mirror or a lens. Various types of lenses can be employed fordifferent applications. All the wavelength channels pass through thebulk optical element in the case of it being a lens, or reflect off thebulk optical element in the case of it being a curved mirror. In someembodiments, such as the embodiment of FIG. 3A, the wavelength channelsall pass through the bulk optical element having optical power twice,once on the way towards the routing elements and once on the way back.In other embodiments, such as those featuring tranmissive switchingelements described below, there are multiple bulk optical elementshaving optical power. However, the constraint that all the wavelengthchannels to be routed pass through each bulk optical element havingoptical power remains the same.

To simplify the description of this embodiment, it is shown as being afour drop ROADM with five wavelength channels, although it is to beunderstood that different numbers of ports and different numbers ofwavelength channels can be accommodated by proper design of the array ofwaveguide dispersive elements and array of switching elements.

In some embodiments, the cylindrical lens 308 is put substantiallyin-between the waveguide device 304 and the switching array 309 wherebythe optical distance between the waveguide device 304 and thecylindrical lens 308 and the optical distance between the cylindricallens 308 and the switching array 309 are each substantially equal to theeffective focal length of the cylindrical lens 308. This system, knownto one skilled in the art as a “4f system” is beneficial to obtain goodcoupling from and to the waveguide element 304 (telecentric imagingsystem). If the micro-mirrors 309 are further able to tilt in the planeperpendicular to that of the figure, a “hitless” operation can beguaranteed by arranging the switching in the subsequent steps of: firstmoving the beams 307 out-of-the plane of the figure (by tilting themicro-mirrors in a plane perpendicular to that of the figure), thensteering the beams 307 to their appropriate location in the plane of thefigure (by tilting the micro-mirrors in the plane of the figure) andfinally establishing the coupling by aligning the beams 307 axis withthat of the substrate of the waveguide device 304 (by tilting themicro-mirrors in a plane perpendicular to that of the figure an oppositeamount to that imparted in the first step of the switching sequence).This switching sequence guarantees that upon switching, the light beams307 only couple to their appropriate output ports and there is nocrosstalk into other output ports.

After being reflected and re-directed by micro-mirrors 309-1 to 309-5,the light beams 307-1 to 307-5 propagate back to the waveguide device304 through cylindrical lenses 308 and 306. Due to the geometry of theabove mentioned 4f system, when the tilt angle of the micro-mirrors 309are properly adjusted, each beam 307-1 to 307-5 can be routed to any ofthe waveguide dispersive elements 305 a to 305 e with good couplingperformance. This is the consequence of the telecentricity of the 4farrangement, which guarantees that the exit angle of the beams 307-1 to307-5 upon exit of the waveguide element 304 and the angle of incidenceof these beams while coming back to the waveguide element 304 areparallel, matching the dispersion requirement for the differentwaveguide dispersive elements 305 a to 305 e. For example, thedemultiplexed beam 307-3 corresponding to 3 is exiting the waveguidedevice 304 from the middle waveguide dispersive element 305 c with 0degree angle. After being routed to MEMS device 309-3 by cylindricallens 308, it is reflected with an angle dependent on the MEMS tiltsetting. In the case depicted on the figure, the mirror sends the beam307-3 upwards. It strikes the upper portion of the cylindrical lens 308and is routed back to the waveguide device 304. With proper selection ofthe tilt angle of the MEMS 309-3, the beam 307-3 is precisely aligned tothe waveguide dispersive element 305 a. Because of the telecentricity ofthe 4f system, the beam 307-3 is incident onto the waveguide dispersiveelement 305 a with again 0 degree angle, which is required for efficientcoupling at wavelength λ₃.

Once all beams 307-1 to 307-5 have re-entered the waveguide device 304at their respective waveguide dispersive elements 305 a to 305 e (in acompletely selectable manner), they are coupled to their respectiveoptical ports 301 a to 301 e.

FIG. 3B shows a side view of the embodiment of FIG. 3A. This showsclearly that cylindrical lens element 303 is substantially re-focussingthe light beam between ports 301 a to 301 e and the waveguide device304, while cylindrical elements 302 a to 302 e have virtually no impacton the light beam in the plane of the figure. The same holds true forcylindrical lens 306 used to substantially collimate light beams 307-1to 307-5 upon exit of the waveguide device 304, while cylindrical lens308 has virtually no effect on light propagation in the plane of thefigure.

In the above embodiment, the routing elements are set to directsubstantially all the light of a given wavelength channel towards theselected output port. In another embodiment, one or more of the routingelements are adapted to controllably misdirect a given wavelengthchannel such that only part of the light is directed to the selectedoutput port, the rest being lost. This allows a wavelength channelspecific attention function to be realized. In yet another embodiment,one or more of the routing elements are adapted to misdirect a givenwavelength channel such that substantially none of the light is directedto any output port. This results in a channel block capability. Themodifications are also applicable to the below-described embodiments.

FIG. 4A shows a hybrid waveguide and MEMS ROADM 400 provided by anotherembodiment of the invention. The embodiment of FIG. 4A is similar tothat of FIG. 3A described above. There are output ports 301 a, 301 b,301 d, 301 e and input port 301 c as before. However, in this embodimentthere is no micro-optic coupling scheme provided external to thewaveguide device for coupling light to and from the input ports to thewaveguide device. Instead, a different waveguide device, generallyindicated at 404 is provided. This waveguide device is the same as thedevice 304 of FIG. 3A with the exception of the fact that it includesintegrated coupling optics 402 a, 402 b, 402 c, 402 d, 402 e forcoupling to and from the waveguide arrays, now designated as 405 athrough 405 e of waveguide device 404, and the ports 301 a through 301e. the remainder of the structure and operation of the embodiment ofFIG. 4A is the same as that described above for FIG. 3A. This enables amore compact design with a more stable relative alignment. It is to beunderstood that arbitrary arrangements of add and drop ports can beprovided without departing from the scope of the invention.

This coupling optics 402 for each waveguide array of dispersive elementsconsists of a slab waveguide ending on an arc where the waveguide arrayof dispersive elements is connected. This arrangement is known to oneskilled in the art as a star coupler (C. Dragone, IEEE PhotonicsTechnology Letters, Vol. 1, No. 8, pp. 241–243, August 1989).

FIG. 4B is a side-view of the embodiment of FIG. 4A.

Referring now to FIGS. 5A and 5B, an alternate embodiment of theinvention employs a stack of waveguide devices 504A to 504E. Thisenables the number of optical ports to be greatly increased. Althoughthe example shown in FIGS. 5A and 5B contains only five stackedwaveguide devices 504A to 504E, yielding 5×5=25 optical ports (from501Aa to 501Ee), it is to be understood that any arbitrary number ofsuch stacked waveguide devices can be used by proper design of theassociated optics elements 506A to 506E and bulk optical element 508,and by providing switching means 509 capable of switching in twodimensions with a large enough tilt angle. Similarly, the choice of a 5wavelength channels system is arbitrary and any larger or lower numberof wavelengths can be routed in the multi-ROADM device 500 byappropriate design of the waveguide dispersive elements 505. In thedescription of FIGS. 5A and 5B, capital letters A to E refer to verticalaxis (plane of FIG. 5B), while lower case letters a to e refer tohorizontal axis (plane of FIG. 5A).

The stacked arrangement of FIGS. 5A and 5B include a respectivewaveguide device 504A through 504E for each layer. Layers 504A, 504B,504D and 504E have respective sets of output ports. The output ports ofdevice 504A are ports 501Aa through to 501Ae. Similarly the output portsof device 504E are ports 501Ea through to 501Ee. The waveguide device504C also has an input port. The input port for device 504C is port501Cc. The remaining ports 501Ca, 501Cb, 501Cd and 501Ce of device 501Care output ports. Thus, there is an array of 25 ports, one of which isan input port (501Cc) and 24 of which are output ports. This is anexample configuration used for description of the invention. Othercombinations of input and output ports are possible without departingfrom the spirit of the invention. In the illustrated embodiment, thereis one input port and the remaining ports are output ports. In anotherembodiment, all of the ports are input ports except one which is anoutput port. In yet another embodiment, there are multiple input portsand multiple output ports. This last arrangement is not fullynon-blocking. Each device 504A to 504E functions in the same manner asdevice 404 of FIG. 4. The arrangement 500 further includes for eachwaveguide device 504A through 504E a respective cylindrical lens 506Athrough 506E. There is also provided a single bulk optical element 508.There is an array of switching elements 509 shown most clearly in theview of FIG. 5A, each of which are capable of tilting in two dimensions,including tilting in the plane of FIG. 5A, and tilting in the plane ofFIG. 5B. Tilting in the plane of 5A allows switching between differentports of the same device 504A to 504E and tilting in the plane of FIG.5B allows switching between ports of different waveguide devices.

Each of the ports (both input and output) are coupled to a respectiveintegrated coupling optics on one of the devices 504A through 504E. Forexample, output port 501Aa is coupled to integrated coupling optics502Aa. It is noted that the embodiment of FIG. 5A could be implementedusing optical elements such as those used in the embodiment of FIG. 3A,instead of using the integrated optics as shown in the illustratedexample.

By way of example, a DWDM light beam containing wavelengths λ₁ . . . λ₅is shown input into the multi-ROADM device 500 at input port 501Cc. Itis coupled to a waveguide dispersive element 505Cc of waveguide device504C through integrated coupling optics 502Cc. The waveguide dispersiveelement consists of an array of waveguides having a predeterminedoptical length difference causing a wavelength dependent exit angle ofthe light upon exit of the waveguide device 504C. Therefore, the lightis demultiplexed in 5 beams comprising respectively λ₁ to λ₅ referenced507-1 to 507-5. On FIG. 5A, only beams 507-2 to 507-4 are shown forclarity. Those beams are substantially collimated in the planeperpendicular to the plane of the figure upon traversing cylindricallens 506C, while being-virtually unaffected in the plane of the figure.The main cylindrical lens 508 is used to route each beam 507-1 to 507-5to a corresponding switching element 509-1 to 509-5, while virtually notimpacting light propagation in the plane perpendicular to the plane ofthe figure. Those switching elements preferably consist of an array oftiltable mirrors capable of tilting both in the plane of the figure andin the perpendicular plane. When the mirrors are tilted in the plane ofthe figure, the light beams 507 can be routed to a particular horizontallocation a to e. When the mirrors are tilted in the perpendicular plane,the light beams 507 can be routed to a particular waveguide device 504Ato 504E in the waveguide stack 504. Therefore, an appropriatecombination of tilt in the plane of the figure and perpendicular to theplane of the figure enables to route each beam 507-1 to 507-5 to any ofthe 25 possible waveguide dispersive elements 505Aa to 505Ee. In apreferred embodiment, the main cylindrical lens 508 is placed in-betweenthe waveguide stack 504 and switching array 509 such that both thewaveguide stack 504 and the switching array 509 lie in the vicinity ofthe focal plane of cylindrical lens 508. This arrangement guaranteesthat irrespective of the tilt of the MEMS mirrors 509-1 to 509-5, lightbeams 507-1 to 507-5 will always have an incident angle in the plane ofthe figure into any of the waveguide dispersive elements 505Aa to 505Eethat maximizes the coupling (i.e. the incident angle is substantiallythe same as the angle upon exit of the input waveguide dispersiveelement 505Cc).

The array of cylindrical lenses 506A to 506E is used to refocus andsteer the light beams 507-1 to 507-5 to their respective waveguidedevice 504A to 504E depending on the switching pattern. In the case ofthe FIGS. 5A and 5B, λ₃ has been arbitrarily switched from waveguidedispersive element 505Cc to waveguide dispersive element 505Aa, λ₄ hasbeen switched from 505Cc to 505Ee and λ₂ has been switched from 505Cc to505Cb. After being coupled to their respective waveguide dispersiveelement 505, the light beams 507 are brought to their respective opticalports 501 through integrated coupling elements 502. In the particularcase of the figure, the 3 depicted wavelengths λ₂ to λ₄ exit atrespectively optical ports 501Cb, 501Aa, and 501Ee.

Referring again to FIG. 5B an important point on this figure is thearrangement of the array of cylindrical lenses 506A to 506E used tosubstantially collimate light beams 507-1 to 507-5 exiting from thewaveguide dispersive element 505Cc in the plane of the figure, while notaffecting light propagation in the perpendicular plane and used tosubstantially re-focus light beams 507-1 to 507-5 when they re-entertheir respective waveguide dispersive element 505Aa to 505Ee dependingon their switching pattern. The optical centre of cylindrical lenses506A to 506E are aligned such that a 0 degree angle of incidence to thewaveguide devices 504A to 504E is obtained when the switching mirrors509 are tilting in the plane of FIG. 5B. For the particular embodimentdepicted on FIGS. 5A and 5B, this is done by offsetting the centre ofcylindrical lenses 506A, 506B, 506D and 506E by an appropriate amount.

FIGS. 6A and 6B show another embodiment of the invention which featurestransmissive switching elements. This embodiment basically consists ofthe input port functionality of FIG. 4 on one side of an array oftransmissive switching elements, on the other side of which is outputport functionality analogous to that provided by device 500 of FIG. 5A.Other embodiments like a 400 type device connected to another 400device, or a 500 type device connected to another 500 type device arepossible, but are not shown.

FIG. 6A shows a top view of a transmissive multi-ROADM device 600comprising a left part (with elements labelled with the suffix “/L” inthe description) and a right part (with elements labelled with thesuffix “/R” in the description) connected through an array oftransmissive switching means 609. A DWDM multiplexed light beamcomprising wavelengths λ₁ . . . λ₅ is input to the transmissivemulti-ROADM at input port 601/L. It is coupled to waveguide dispersiveelement 605/L through integrated coupling element 602/L. Due to thedispersion imparted by waveguide dispersive element 605/L, the lightexits the waveguide device 604/L with an angle dependent on wavelength.For clarity, only three wavelengths are shown as beams 607-2 to 607-4corresponding to λ₂ to λ₄ respectively, although all five wavelengthchannels are present. The light beams 607-1 to 607-5 are substantiallycollimated in the plane perpendicular to the plane of the figure bycylindrical lens 606/L. The main cylindrical lens 608/L is used to routethe different wavelength channels to a transmissive switching meansarray 609-1 to 609-5. These switching elements are capable of steering alight beam in transmission. For example, an optical phase array, anelectro-hologram or other phase elements are known by one skilled in theart to provide this steering function. After being steered by thetransmissive switching means 609-1 to 609-5, the light beams 607-1 to607-5 are directed towards the waveguide stack 604/R by the maincylindrical lens 608/R. Preferably, the main cylindrical lenses 608/Land 608/R are assembled to provide a 4f system, whereby the waveguidedevice 604/L and the array of switching means 609 are lying on the focalplanes of cylindrical lens 608/L and the array of switching means 609and the waveguide stack 604/R are lying on the focal planes ofcylindrical lens 608/R. This arrangement guarantees that irrespective ofthe switching performed by switching elements 609, every wavelengthchannel 607-1 to 607-5 has the proper angle of incidence in the plane ofthe figure to maximize coupling into the waveguide stack 604/R. In theparticular case when lens 608/L and 608/R have the same focal length,this corresponds to the angles of incidence to the waveguide stack 604/Rbeing opposed to the exit angles from waveguide device 604/L and thewaveguide dispersive elements 605/R being mirror images of the waveguidedispersive element 605/L. Other combinations using different focallengths for cylindrical lenses 608/L and 608/R and different designs forwaveguide dispersive elements 605/L and 605/R are possible by properdesign. The array of cylindrical lenses 606A/R to 606E/R is used torefocus the light beams 607-1 to 607-5 into their respective waveguidedispersive element 605/R depending upon switching. In the example shownon FIG. 6, the wavelength channels λ₂ to λ₄ are arbitrarily routedrespectively to waveguide dispersive elements 605Cb/R, 605Aa/R and605Ee/R. After being routed to their respective waveguide dispersiveelements, the light beams 607-1 to 607-5 are connected to theirrespective optical ports 601/R through respective integrated couplingmeans 602/R.

FIG. 6B shows a side view of the embodiment of FIG. 6A. It shows inparticular that the cylindrical lens 606/L is used to substantiallycollimate the light beams 607-1 to 607-5 exiting the waveguide device604/L. After traversing the array of transmissive switching means 609,the light beams 607-1 to 607-5 are steered in two dimensions. In theplane of FIG. 6B, the beam 607-3 is tilted upwards towards waveguidedevice 604A/R, the beam 607-4 is tilted downwards towards waveguidedevice 604E/R, while the beam 607-2 is not deflected and is connected towaveguide device 604C/R. In order to couple efficiently to theirrespective waveguide device 604/R, the light beam 607-1 to 607-5 arere-focussed through the array of cylindrical lenses 606/R. In order tocouple efficiently to waveguide device 604/R, it is also necessary thatthe light beams 607-1 to 607-5 be parallel to the substrates of theircorresponding waveguide devices 604/R. This is achieved by properpositioning of the optical centre of cylindrical lenses 606/R. In theexample shown on FIG. 6B where all waveguide substrates 604A/R to 604E/Rare parallel and horizontal, this is achieved by having the opticalcentre of cylindrical lenses 606A/R, 606B/R, 606D/R, and 606E/R offsetby a proper amount compared to the waveguide core locations.

FIG. 7 shows an example schematic layout of a waveguide device 704containing an array of waveguide dispersive elements 705 designed for a40 channels system with 100 GHz spacing. This might be used to implementwaveguide device 404 of FIG. 4A or devices 504A through 504E of FIG. 5Afor example. The waveguide device 704 consists of optical ports 701 a to701 e coupled to waveguide dispersive elements 705 a to 705 e throughintegrated coupling elements 702 a to 702 e. The coupling elements 702 ato 702 e each comprise a free propagating region in the plane of thefigure, guiding the light only in the perpendicular plane. The length ofthis free propagation region in this example is 13.63 mm, ending with anarc of 13.63 mm radius of curvature. The waveguide dispersive elements705 a to 705 e each consist of an array of 250 waveguides (not allshown) connected at one end to this arc with a spacing of 12 microns andon the other end to the facet of the waveguide device 704 with a spacingof 12 microns. The 250 waveguides are arranged such that there is aconstant physical path length difference between each consecutivewaveguide of 25.55 microns. With these design parameters, a 40 channel100 GHz spacing DWDM multiplexed light beam input at 701 c into thewaveguide device 704 is demultiplexed into 40 light beams 707-1 to707-40 upon exit of the waveguide dispersive element 705 c with an angledepending on wavelength of about 1.4 radian per micron. The derivationof the chosen design parameters are similar to those required for an AWGand is known to one skilled in the art (see for example H. Takahashi etal., Journal of Lightwave Technology, Vol. 12, No. 6, pp. 989–995, 1994)with the only difference that the array of waveguides 705 ends on thestraight facet of waveguide device 704.

FIG. 8A to FIG. 8C show an example of the far field of light beams707-1, 707-20 and 707-40 emitted from the waveguide dispersive element705 c designed according to parameters mentioned in the abovedescription of FIG. 7 for three different wavelengths of lightcorresponding to a frequency of 192 THz (λ₁=1561.419 nm), 194 THz(λ₂₀=1545.322 nm) and 196 THz (λ₄₀=1529.553 nm) respectively. As can beseen on the graph, the light is substantially collimated in the plane ofthe figure (which is also the plane of FIG. 7) and has an angle ofincidence exiting the waveguide device 704 depending on wavelength.

FIG. 9A shows the beam 707-20 after being focussed through a lens withan effective focal length of 5 mm. This focussing would typically resultfrom traversing cylindrical lens 408 in the preferred embodimentdescribed in FIG. 4A, although in this last case, the effective focallength of the main cylindrical lens 408 could differ depending on thelimitation in the minimum spacing of the switching elements 409 withtypical practical focal length ranging from 60 mm to 150 mm. The focallength of lens 306 is then determined to enable beam propagation fromwaveguide element 404 to switching elements 309. This would typicallyrequire a focal length of between 2 and 5 mm. These are example rangesonly. Actual values can be determined on a per application basis.

FIG. 9B shows the same data as FIG. 9A, superimposing focussed beams707-1, 707-20 and 707-40.

FIG. 10A shows the top view of another embodiment as per the inventiongenerally indicated at 1000. This embodiment is similar to that of FIG.4A in that a set of ports 301 a through 301 e are provided which areconnected through integrated optical coupling means to waveguide arrays.In this example, the integrated coupling means are designated withreference numerals 1002 a through 1002 e and the waveguide arrays aredesignated as 1005 a through 1005 e, forming part of a waveguide device1004. This embodiment differs from that of FIG. 4A in that there is nomain cylindrical lens element 308, but rather the functionality of thatlens is integrated with the waveguide dispersive elements. This isachieved by putting the appropriate phase profile inside the waveguidedispersive element. In the case of a waveguide array, this is usuallyachieved through the addition of an extra parabolic phase term to thelinear phase term required for dispersion only. Such a focussing anddispersive arrangement of a waveguide element is described, for example,in: M. K. Smit, Electronics Letters, Vol. 24, pp. 385–386, 1988. In theparticular case of the present invention though, the focussingparameters of each of the waveguide dispersive element array 1005 a to1005 e have to be computed such that all wavelengths channels 1007-1through 1007-4 are focussed to the same point on the switching array1009-1 to 1009-5. This is achieved by putting an appropriate offset inthe parabolic phase profile for each respective waveguide dispersiveelement. Cylindrical lens 1006 performs the same function as lens 306 ofFIG. 4A. For the description of FIG. 10A, a five wavelengths system hasbeen shown with an array of five waveguide dispersive elements, althoughother combinations are possible.

By way of example, an optical signal containing λ₁ to λ₅ is input to thewavelength switch device 1000 through optical port 301 c. It is coupledto integrated lens-waveguide dispersive element 1005 c of waveguidedevice 1004 through integrated coupling optics 1002 c. The preferredembodiment of the waveguide dispersive element is an array of waveguidehaving a predetermined phase relationship with each other. The linearterm in this phase profile accounts for dispersion, while the secondorder terms add focussing power. Therefore, the light beams exiting thewaveguide device 1004 have a diversity of angles depending onwavelengths and are all focussed on the focal plane of integratedlens-waveguide dispersive element 1005 c. For clarity, only three suchbeams 1007-2 to 1007-4 are shown on the figure. While the beams arefocussed in the plane of the figure through the non-linear phase profileimparted on the array of waveguides constituting the integratedlens-waveguide dispersive element 1005 c, the light beams 1007-1 to1007-5 are diverging in the plane perpendicular to that of the figure.Therefore, a cylindrical lens 1006 is provided that collimates the beam1007-1 to 1007-5 in the plane perpendicular to that of the figure, whilesubstantially not affecting light propagation in the plane of thefigure. In the plane of the figure, there is no optical element havingpower, therefore this region labelled 1010 is referred to as afree-space propagation region. As mentioned above, all integratedlens-waveguide dispersive elements 1005 a to 1005 e are designed suchthat all wavelengths channels are focussed onto the same pointirrespective of the lens-waveguide dispersive elements they arepropagating through. This is achieved through appropriate design of thenon-linear terms within the phase profile inside each of the waveguidearray constituting the integrated lens-waveguide dispersive elements1005 a to 1005 e. In particular, the switching means array 1009-1 to1009-5 is lying substantially in the common focal plane of theseintegrated lens-waveguide dispersive elements 1005 a to 1005 e.

The switching means 1009-1 to 1009-5 are shown on FIG. 10A asmicro-mirrors, although other arrangements are possible withtransmissive switching means for example. Upon tilting of themicro-mirrors, the light beams 1007-1 to 1007-5 can be routed from themiddle integrated lens-waveguide dispersive element 1005 c to any of thearray of integrated lens-waveguide dispersive elements 1005 a to 1005 e.With the particular geometry chosen for this embodiment, the couplingefficiency is maximum. This will be explained in the case of light beam1007-2, but is true simultaneously for all light beams 1007-1 to 1007-5.

Light beam 1007-2 corresponds to wavelength channel λ₂ as it exits thewaveguide device 1004 through the end facet of integrated lens-waveguidedispersive element 1005 c. Given the design parameters mentioned above,it is focussed on switching element 1009-2. If this light beam wouldhave originated from integrated lens-waveguide dispersive element 1005b, it would also have been focussed to switching element 1009-2, due tothe particular of the optical design of the integrated lens-waveguidedispersive element 1005 b. Therefore, one can establish an optical pathfrom 1005 c to 1005 b for wavelength channel λ₂ by tilting micro-mirror1009-2 by an appropriate amount. This is essentially true for allwavelength channels and all integrated lens-waveguide dispersiveelements.

Upon coupling back to waveguide device 1004, the light beams 1007-1 to1007-5 are connected to their respective output ports 301 a to 301 edepending on the switching pattern chosen for switch array 1009, throughintegrated optics coupling means 1002 a to 1002 e. In the case shown onFIG. 10 a, wavelength channel λ₂ is directed to port 301 b, wavelengthchannel λ₃ is directed to port 301 a and wavelength channel λ₄ isdirected to port 301 e.

FIG. 10B shows a side view of the embodiment shown on FIG. 10A. In thiscase, there is only one cylindrical lens 1006 used to substantiallycollimate light beams 1007-1 to 1007-5 upon exit of the waveguide device1004 and to re-focus them on their way back to waveguide device 1004.

Referring now to FIG. 12, shown is a system block diagram of afree-space embodiment of a wavelength selective optical switch providedby the invention. This embodiment employs an array of reflectivediffraction gratings instead of waveguide devices as employed in theprevious embodiments. More generally, non-transmissive dispersiveelements can be employed with this arrangement. The figure shows a setof MLA's (microlens array) 1302, the output of which passes through arouting lens 1304. The top view of the device is generally indicated at1300TOP and the side view is generally indicated at 1300SIDE.

The output of the routing lens 1304 passes through free-space to a mainlens 1306 which routes each of the ports to a respective diffractiongrating forming part of an array of diffraction gratings 1307. The arrayof diffraction gratings reflect the incoming light of each portaccording to wavelength. There is an array of switching means 1308 shownto consist of tiltable mirrors 1308 a, 1308 b and 1308 c. There would bea respective switching element for each wavelength. It is noted that theswitching elements 1308 are not in the same horizontal plane as therouting lens 1304. This can be most clearly seen in the side view1300SIDE. Each switching element performs a switching of light of agiven wavelength from one input port to another optical port by tiltingof the mirror.

The operation of FIG. 12 is similar to that of previous embodiments. Oneof the ports is designated as an input port and the other ports areoutput ports. By appropriate tilting of the mirrors in array 1308, eachwavelength of a multi-wavelength input signal received at the input portcan be switched to any of the output ports.

FIG. 13 is an implementation similar to that of FIG. 12 except that inthis case, there is a two dimensional array of ports, generallyindicated at 1400 optically connected through routing lens 1402 to themain lens 1406 and array of diffraction gratings 1408. Switching/routingis performed using routing elements generally indicated at 1404. Thisembodiment is similar functionally to the embodiment of FIG. 5A, butwith diffraction gratings used as dispersive elements.

The above described embodiments have employed either an array ofwaveguides or diffraction grating as the dispersive elements. It isnoted that any appropriate diffraction grating type might be employed.For example reflective, transmissive, echelle, echellon, or grisms, toname a few examples. Array waveguides and echelle waveguide gratingsmight be employed. Prisms might instead be employed for the dispersiveelements. more generally, any dispersive element that can achieve thedesired wavelength dependent function may be employed by embodiments ofthe invention.

The described embodiments have featured MEMS mirror arrays to performthe switching of wavelengths. More generally, any appropriate switchingmeans may be used. For example, liquid crystal beams steering elements(phase array), accouto-optic beam deflectors, solid-state phase array,controllable holograms, periodically polled Lithium Niobate beamdeflectors.

Since the index of refraction in waveguides is a function oftemperature, the dispersive properties of the waveguide based dispersiveelement are varying with temperature, causing the beams of light for aparticular channel to move away from its corresponding mirror centerposition. It is desirable to provide compensation for this variation asa function of temperature. One way to compensate for this effect is tomount the mirror array on some dual material mount, whereby the mirrorarray moves with the beams as the temperature changes. This is achievedfor example when using a mount material for the main support piece thathas the same coefficient of thermal expansion as Silicon, and putting anextra piece of high expansion material (for example Aluminum) betweenthis main support piece and the MEMS mirror array. The exact dimensionof this extra piece depends on the coefficient of thermal expansion ofthe material for this extra piece, on the focal length of the maincylindrical lens and on the dispersion characteristics of the waveguidedispersive element. An example of this is shown in FIG. 14 which showsthe device 400 of FIG. 4 mounted on a main support piece 1500. The MEMSarray 309 is mounted on a MEMS support element 1502 which moves the MEMSmirrors up and down as a function of temperature in sync with light beam307. An alternative mount is shown on FIG. 15, in which the waveguideelement itself is tilted in front of the optics assembly. Again, this isachieved by inserting an extra support piece 1602 having a differentcoefficient of thermal expansion than the main support piece at one endof the waveguide element. The exact dimension and location of this extrasupport element is designed as to cancel any temperature dependentdispersion variation with the net effect that the angle that a lightbeam of a particular wavelength enters and exits the waveguide element400 is substantially constant over a wide temperature range. Both theembodiments of the FIGS. 14 and 15 can be employed with any of thewavelength selective switches described herein.

In the presence of a small amount of residual birefringence in thewaveguide dispersive element, the TE part of light beam and the TM partof a light beam of a particular wavelength do not exactly overlap on amirror in the mirror array. To compensate for this effect, someembodiments feature a birefringent crystal beam displacer in the beampath to make the two TE and TM subbeams coincide on the array ofmirrors. FIG. 17 shows an example of this applied to the embodiment ofFIG. 4 again. A birefringent crystal 1700 is shown inserted between themain lens 308 and the array of MEMS mirrors 309. This modification canbe employed for any of the above described embodiments.

In the presence of some small residual polarization dependence of any ofthe components in the device as per the invention, that manifests itselfas a polarization dependent transmission efficiency through the device.In some embodiments, a quarter-wave plate is inserted in the opticalpath with the effect to swap TE and TM sub beams in the middle of thedevice. This causes the losses for the two polarization axis to beaveraged out (TE/TM or TM/TE). An example of this is shown in FIG. 18applied to the device 400 of FIG. 4. Here a quarter-wave plate 1800 isshown inserted between the main lens 308 and the array of MEMS mirrors309.

Furthermore, although the preceding descriptions have only mentionedswitching applications in which routing elements having a switchingfunction are used to established re-programmable light paths, in otherembodiments fixed arrangements are also possible to establish permanentlight paths using routing elements which do not switch. The applicationsfor such fixed devices would be for fixed demultiplexers, filters, bandfilters, interleavers, etc.

The above-described embodiments have all focused on the redirection oflight from an input to an output port, thereby realizing wavelengthselective switching. Another embodiment of the invention provides anintegration platform having three or more ports, a dispersive elementper port, and a bulk optical element having optical power incommunication with all of the ports. An example implementation is thearrangement of FIG. 3 not including the switching elements. Such anarrangement can be employed for many purposes other than switching. Forexample, by replacing the switching elements with appropriate lightprocessing elements, a channel selective filtering function, limiting,optical sensing, channel attenuation, polarization state changeapplication can be achieved.

The invention is not intended to be limited to the above mentionedspecific embodiments but should rather be understood as being within thescope of the appended claims.

1. An apparatus comprising: a plurality of optical ports including aninput optical port for receiving an optical signal with a plurality ofwavelength channels, and a plurality of output ports; for each opticalport, a respective waveguide dispersive element optically connected tothe optical port, the dispersive elements integrated on a same waveguidedevice in a first plane; a bulk optical element having optical power; aplurality of non-transmissive routing elements; wherein the dispersiveelement of the input port disperses each of the wavelength channels at adifferent respective exiting angle dependent upon wavelength, whereinthe bulk optical element redirects each one of the wavelength channelsat a respective angle towards a respective one of said plurality ofrouting elements, and wherein said plurality of routing elements directseach of the wavelength channels via the bulk optical element to aselected output port in the first plane via the respective dispersiveelement of the selected output at a respective angle of incidencedependent upon the selected output port.
 2. The apparatus of claim 1,wherein at least one routing element is also controllable so as toredirect only a portion of one of the wavelength channels to realize anattenuation function.
 3. The apparatus of claim 1, wherein at least onerouting element is also controllable so as to redirect all of one of thea wavelength channels to realize a channel block function.
 4. Theapparatus of claim 1, wherein the dispersive elements are transmissive,and are disposed between the optical ports and the bulk optical element.5. The apparatus of claim 1, wherein each routing element is staticallyconfigured to direct light to a respective specific output port.
 6. Theapparatus of claim 1, wherein each routing element is dynamicallyconfigurable to switch light to any output port.
 7. The apparatus ofclaim 1, wherein each dispersive element comprises an array ofwaveguides having a predetermined optical path length difference spreadacross the array.
 8. The apparatus of claim 1, further comprisingadditional output optical ports, each with a respective additionaldispersive element; wherein a plurality of the additional dispersiveelements are integrated into an additional waveguide device in a secondplane, parallel to the first plane; wherein each routing element is amicro-mirror tiltable in two dimensions.
 9. The apparatus of claim 1,further comprising micro-optics coupling elements adapted to couplelight from each port to/from the respective dispersive element.
 10. Theapparatus of claim 1 wherein each dispersive element comprises atransmissive diffraction grating.
 11. The apparatus according to claim1, wherein the dispersive elements and the routing elements are placedsubstantially at focal planes of the bulk optical element; whereby eachwavelength channel re-enters the waveguide device at an angle ofincidence substantially equal to their respective exiting angle,providing increased coupling efficiency.
 12. The apparatus according toclaim 1 wherein the bulk optical element having optical power is a lensor a curved mirror.
 13. The apparatus according to claim 1, wherein thebulk optical element comprises a main cylindrical lens element adaptedto focus light in a first plane in the plane of the wavelengthsubstrate, the apparatus further comprising a transverse cylindricallens adapted to substantially collimate light in a second planeperpendicular to the first plane.
 14. The apparatus according to claim13, wherein the main cylindrical lens has a focal length such that thedispersive elements are in a focal plane of the lens on a first side ofthe lens, and the routing elements are in a focal plane of the lens on asecond side of the lens; whereby each wavelength channel re-enters thewaveguide device at an angle of incidence substantially equal to theirrespective exiting angle providing increased coupling efficiency. 15.The apparatus of claim 1 wherein the dispersive elements are selectedfrom a group comprising: echelle grating, echellon gratings, prisms,arrayed waveguides.
 16. The apparatus of claim 5 wherein each routingelement is a tiltable micro-mirror.
 17. The apparatus of claim 5 whereineach routing element is one of a liquid crystal beam steering element,an acousto-optic beam deflector, part of a solid state phase array, acontrollable hologram, a periodically polled Lithium Niobate beamdeflector.
 18. The apparatus of claim 1, further comprising: an athermalmount for the routing elements adapted to shift the routing elements tocompensate for changes in dispersive characteristics of the dispersiveelements as a function of temperature.
 19. The apparatus of claim 1,further comprising: an athermal mount for the dispersive elementsadapted to tilt the dispersive elements to compensate for changes indispersive characteristics of the dispersive elements as a function oftemperature such that light exiting the dispersive elements issubstantially centered on the routing elements.
 20. The apparatus ofclaim 1, further comprising: a birefringent crystal beam displacerbetween the dispersive elements and the routing elements adapted tocompensate for birefringence of the dispersive elements so as to make TEand TM sub-beams substantially coincide on the routing elements.
 21. Theapparatus of claim 1, further comprising: a quaffer wave plate in anoptical path of the switch adapted to swap TE and TM sub-beams to causelosses for TE and TM polarization axes to be substantially averaged out(TE/TM or TM/TE).
 22. The apparatus of claim 1, wherein the bulk opticalelement is a lens, each dispersive element is non-transmissive and theoptical ports and routing elements are arranged on a first side of thelens and the dispersive elements are on a second side of the cylindricallens.
 23. The apparatus of claim 22 wherein the dispersive elementscomprise non-transmissive diffraction gratings.
 24. An apparatuscomprising: a plurality of optical ports including an input optical portfor receiving an input optical signal with a plurality of wavelengthchannels, and at least two output optical ports; for each optical port,a respective dispersive element optically connected to the optical port,the dispersive elements of the output optical ports being integrated ona first waveguide substrate in a first plane; a plurality oftransmissive routing elements; a first bulk optical element havingoptical power; and a second bulk optical element having optical power;wherein the dispersive element of the input port disperses thewavelength channels in the input optical signal at respective exitingangles dependent upon wavelength, and wherein the first bulk opticalelement redirects each one of the wavelength channels at a respectiveangle towards a respective one of said plurality of transmissive routingelements, and wherein, for each wavelength channel the respective one ofsaid plurality of transmissive routing elements directs said wavelengthchannel in the first plane via the second bulk optical element to arespective selected port of said output ports via the respectivedispersive element of the selected output port at a respective angle ofincidence dependent upon the selected output port.
 25. The apparatus ofclaim 24 wherein each transmissive routing element is staticallyconfigured to direct light to a respective specific output port.
 26. Theapparatus of claim 24 wherein each transmissive routing element isdynamically configurable to switch light to any output port.
 27. Theapparatus of claim 24 wherein each dispersive element comprises an arrayof waveguides having a predetermined optical path length differencespread across the array.
 28. The apparatus of claim 27, furthercomprising additional output ports with a respective dispersive elementoptically connected thereto; wherein the dispersive elements of theadditional output ports are integrated onto a second waveguide device ina second plane forming a stack of waveguide devices; and wherein eachrouting element is a micro-mirror tiltable in two dimensions.
 29. Theapparatus of claim 24 further comprising micro-optics coupling elementsadapted to couple light from each port to/from the respective dispersiveelement.
 30. The apparatus of claim 24 further comprising integratedoptical coupling elements adapted to couple light from each port to/fromthe respective dispersive element.
 31. The apparatus of claim 30 whereinthe integrated optical coupling element comprise star couplers.
 32. Theapparatus according to claim 24 wherein the dispersive element of theinput port is placed substantially at a focal plane of the first bulkoptical element having optical power, and the dispersive elements of theoutput ports are placed substantially at a focal plane of the secondbulk optical element having optical power, and the routing elements arealso at a focal distance from both the first and second bulk opticalelements, whereby each wavelength channel re-enters the waveguide deviceat an angle of incidence substantially equal to or opposite theirrespective exiting angle providing increased coupling efficiency. 33.The apparatus according to claim 24 wherein the first bulk opticalelement and the second bulk optical element are each a lens or, a curvedmirror.
 34. The apparatus according to claim 28, wherein: the first bulkoptical element comprises a first main cylindrical lens adapted to focuslight in the first plane; and the second bulk optical element havingoptical power comprises a second main cylindrical lens adapted to focuslight in the second plane; the apparatus farther comprising: a firsttransverse cylindrical lens adapted to substantially collimate light ina third plane perpendicular to the first plane; and a second transversecylindrical lens adapted to substantially collimate light in a fourthplane perpendicular to the second plane.
 35. The apparatus according toclaim 34, wherein the first main cylindrical lens has a focal lengthsuch that the dispersive element of the input port is in a first focalplane of the first main cylindrical lens on a first side of the firstmain cylindrical lens, and the transmissive routing elements are in asecond focal plane of the first main cylindrical lens on a second sideof the first main cylindrical lens; and wherein the second maincylindrical lens has a focal length such that the dispersive elements ofthe output port are in a first focal plane of the second maincylindrical lens on a first side of the second main cylindrical lens,and the transmissive routing elements are in a second focal plane of thesecond main cylindrical lens on a second side of the second maincylindrical lens.
 36. The apparatus of claim 24 wherein the waveguidedispersive elements are selected from a group comprising: echellegrating, echellon gratings grisms, prisms, arrayed waveguides.
 37. Theapparatus of claim 24 farther comprising: an athermal mount for therouting elements adapted to shift the routing elements to compensate forchanges in dispersive characteristics of the dispersive elements as afunction of temperature.
 38. The apparatus of claim 24 farthercomprising: a first athermal mount for the dispersive element of theinput port adapted to tilt the dispersive element of the input port tocompensate for changes in dispersive characteristics of the dispersiveelement as a function of temperature such that light exiting thedispersive elements is substantially centered on the transmissiverouting elements; and a second athermal mount for the dispersiveelements of the output ports adapted to tilt the dispersive elements ofthe output ports to compensate for changes in dispersive characteristicsof the dispersive elements as a function of temperature such that lightexiting the transmissive routing elements is accurately aligned with thedispersive elements of the output ports.
 39. The apparatus of claim 24further comprising: a first birefringent crystal beam displacer betweenthe dispersive element of the input port and the routing elementsadapted to compensate for birefringence of the dispersive element of theinput port so as to make TE and TM sub-beams substantially coincide onthe routing elements; and a second birefringent crystal beam displacerbetween the dispersive elements of the output port and the routingelements adapted to compensate for birefringence of the dispersiveelements of the output ports so as to make TE and TM sub-beam'ssubstantially coincide on the routing elements.
 40. The apparatus ofclaim 24 further comprising: a first quarter wave plate in an opticalpath of the switch on a first side of the transmissive routing elementsadapted to swap TE and TM sub-beams to cause losses for TE and TMpolarization axes to be substantially averaged out (TE/TM or TM/TE); anda second quarter wave plate in an optical path of the switch on a secondside of the transmissive routing elements adapted to swap TE and TMsub-beams to cause losses for TE and TM polarization axes to besubstantially averaged out (TE/TM or TM/TE).
 41. The apparatus of claim24 wherein the dispersive elements are non-transmissive.
 42. Anapparatus comprising: a stacked plurality of rows of optical ports, theports comprising: an input optical port for receiving an input opticalsignal with a plurality of wavelength channels; and a plurality ofoutput optical ports; for each optical port, a respective dispersiveelement optically connected to the optical port, forming rows ofmultiple dispersive elements, wherein each row of dispersive elements isintegrated on a different waveguide device, forming a stack of waveguidedevices in parallel planes; a bulk optical element having optical power;a plurality of routing elements; wherein the dispersive element of theinput port disperses each of the wavelength channels at a differentrespective exiting angle dependent upon wavelength in a first plane;wherein the bulk optical element redirects each of the the wavelengthchannels towards a respective one of the plurality of routing elements,and wherein the plurality of routing elements directs each of saidwavelength channels via the bulk optical element to a respectiveselected output port in the first plane or one of the planes parallelthereto via the respective dispersive element of the selected outputport at a respective angle of incidence dependent upon wavelength andthe selected output.
 43. The apparatus of claim 42 wherein each routingelement is statically configured to switch light to a respectivespecific output port.
 44. The apparatus of claim 42 wherein each routingelement is dynamically configurable to switch light to any output port.45. The apparatus of claim 42 wherein each dispersive element comprisesan array of waveguides having a predetermined optical path lengthdifference spread across the array.
 46. The apparatus of claim 42further comprising micro-optics coupling elements adapted to couplelight from each port to/from the respective dispersive element.
 47. Theapparatus of claim 42 further comprising integrated optical couplingelements adapted to couple light from each port to/from the respectivedispersive element.
 48. The apparatus of claim 47 wherein the integratedoptical coupling element comprise star couplers.
 49. The apparatus ofclaim 42 wherein each dispersive element comprises a diffractiongrating.
 50. The apparatus according to claim 42, wherein the dispersiveelements and the routing elements are placed substantially at focalplanes of the bulk optical element having optical power, whereby eachwavelength channel re-enters the waveguide device at an angle ofincidence substantially equal to or opposite their respective exitingangle providing increased coupling efficiency.
 51. The apparatusaccording to claim 42 wherein the bulk optical element having opticalpower is a lens or a curved mirror.
 52. The apparatus according to claim42, wherein: the bulk optical element having power comprises a maincylindrical lens element adapted to focus light in a first plane in theplane of the waveguide device substrates; the apparatus furthercomprising: for each waveguide device, a respective transversecylindrical lens adapted to substantially collimate light in arespective second plane perpendicular to the plane of the waveguidedevice substrates.
 53. The apparatus according to claim 52, wherein themain cylindrical lens has a focal length such that the dispersiveelements are in a focal plane of the lens on a first side of the lens,and the routing elements are in a focal plane of the lens on a secondside of the lens, whereby each wavelength channel re-enters thewaveguide device at an angle of incidence substantially equal to oropposite their respective exiting angle providing increased couplingefficiency.
 54. The apparatus of claim 42 wherein the dispersiveelements are selected from a group comprising: echelle grating, echellongratings grisms, prisms, arrayed waveguides.
 55. The apparatus of claim42 wherein each routing element is a micro-mirror tiltable in twodimensions.
 56. The apparatus of claim 42 wherein each routing elementis one of a liquid crystal beam steering element, an acousto-optic beamdeflector, part of a solid state phase array, a controllable hologram, aperiodically polled Lithium Niobate beam deflector.
 57. The apparatus ofclaim 42 further comprising: an athermal mount for the routing elementsadapted to shift the routing elements to compensate for changes indispersive characteristics of the dispersive elements as a function oftemperature.
 58. The apparatus of claim 42 further comprising: anathermal mount for the dispersive elements adapted to tilt thedispersive elements to compensate for changes in dispersivecharacteristics of the dispersive elements as a function of temperaturesuch that light exiting the dispersive elements is substantiallycentered on the routing elements.
 59. The apparatus of claim 42 furthercomprising: a birefringent crystal beam displacer between the dispersiveelements and the routing elements adapted to compensate forbirefringence of the dispersive elements so as to make TE and TMsub-beams substantially coincide on the routing elements.
 60. Theapparatus of claim 42 further comprising: a quarter wave plate in anoptical path of the switch adapted to swap TE and TM sub-beams to causelosses for TE and TM polarization axes to be substantially averaged out(TE/TM or TM/TE).